Counseling self-efficacy is an important indicator in counseling field because it is associated with many counseling-related factors such as counseling competence and counseling outcome. Therefore, it is important to successfully measure counseling self-efficacy of counselors-in-training so that counselor educators can assess counselors-in-trainings' developmental stage by understating their counseling self-efficacy level and can better educate them by providing opportunities fulfill necessary experiences that can enhance counseling self-efficacy. There have been different counseling self-efficacy scales; however, most of them focused directly on counselors' skills, knowledge, and confidence. Also, none of the scales fully reflected Bandura's self-efficacy theory with four sources (i.e., mastery experience, vicarious experience, social persuasion, physiological and emotional state) except one scale. Even the one scale was a modified version of mathematics self-efficacy scale developed in Malaysia, so it did not consider the perspectives of counselors-in-training in the United States. The purpose of this Delphi study was to develop a potential list of items that can assess counseling self-efficacy of counselors-in-training based on Bandura's self-efficacy theory. A total of 12 experts who are counselor educators completed the three rounds of surveys. Four research questions were included in Round One survey and guided the current study. The questions were as follows: (a) what are the perceived mastery experiences that can contribute to counseling self-efficacy of counselors-in-training during their training in a counseling program? (b) what are the perceived vicarious experiences that can contribute to counseling self-efficacy of counselors-in-training during their training in a counseling program? (c) what are the perceived social persuasion situations that can contribute to counseling self-efficacy of counselors-in-training during their training in a counseling program? and (d) what are the perceived physiological and emotional state situations that can contribute to counseling self-efficacy of counselors-in-training during their training in a counseling program? As a result, 32 items were developed for the potential scale of counseling self-efficacy for counselors-in-training, including six items for mastery experience, six items for vicarious experience, 11 items for social persuasion, and nine items for physiological and emotional state. Interpretations of the results and relevant implications for counseling programs, counselor educators, and future research are discussed. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]